Wireless power transmission or wireless energy transfer technology which wirelessly transfers electric energy already started in 1800 with the use of an electric motor or a transformer using a principle of electromagnetic induction. Then, methods of transmitting electric energy by emitting electromagnetic waves such as radio waves or lasers were tried. Electric toothbrushes or some of wireless razors that we frequently use are actually charged using the principle of electromagnetic induction. Electromagnetic induction refers to a phenomenon in which a voltage is induced and a current flows when a magnetic field is changed around a conductor. The electromagnetic induction method is being rapidly commercialized, but it has a disadvantage of a short transmission distance of power.
Up to now, an energy transfer method using a wireless method includes a long range transmitting technology and the like using resonance and a short wave wireless frequency in addition to electromagnetic induction.
Recently, an energy transfer method using resonance of the wireless power transmission technology is being widely used.
In a wireless power transmission system using resonance, power is transferred through coils of a transmission side and a receiving side, and therefore the user can easily charge electronic apparatuses such as mobile apparatuses.
A wireless power transmitter transmits power having a frequency band for every wireless power transmitter to a receiver. In this case, a wireless power receiver is configured to match a corresponding frequency band, and is able to receive only a power of a specific frequency band. That is, in the conventional art, when a frequency band of power transmitted by the wireless power transmitter is changed, there is a problem that the wireless power receiver cannot correctly receive the power.